Effect and controlling mechanism of vanadium on Fe-Al interface reaction in Al-Zn bath

The influence of vanadium on Fe-Al interface reaction of steels during hot-dip process was investigated by immersing low carbon steel plates into six different Al and Al-Zn baths at 730 degrees C and 620 degrees C. The microstructure and phase constituent of the formed coatings were analyzed with SEM-EDS and XRD. The intermetallic layers formed on the steel plate surfaces in Al bath consist of Fe2Al5 and FeAl3 phases. As 0.05 wt.% V was added to the Al bath, the Fe2Al5 layer became thinner. Whereas the steel plates were immersed into 55%Al-Zn bath, a periodic laminar structure, containing FeAl3 and AI-Zn phases, formed. However, the periodic laminar structure disappeared and a continuous thin Fe2Al5 layer appeared as V was added into Galvalume bath, and the whole intermetallic layer consists of Fe2Al5, Fe2Al8Si and FeAl3 phases. The presence of 0.05 wt.% V in the bath promoted the formation of Fe2Al5 layer, As it covers the whole steel plate surface, it retards the further Fe-Al reaction in the bath, leading to a thin intermetallic layer. The influence of V on Fe-Al interface reaction was studied by means of Vienna Ab-initio Simulation Package (VASP) based on first-principles method. The exchange energy, bonding energy, charge density differences and electronic density of states of Fe-2(Al,V-3)(5) and Fe(Al,V-12)(3) are analyzed. Both the experimental results and theoretical calculation results show that V could occupy the vacancies of Fe2Al5 lattice which could promote the nucleation of Fe2Al5, and therefore it suppresses the growth of Fe-Al phase. (C) 2015 Elsevier B.V. All rights reserved.